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73. Set Matrix Zeroes

Medium

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0’s, and return the matrix.

You must do it in place.

Example 1:

Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]

Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]

Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

Constraints:

• m == matrix.length
• n == matrix[0].length
• 1 <= m, n <= 200
• -231 <= matrix[i][j] <= 231 - 1

Follow up:

• A straightforward solution using O(mn) space is probably a bad idea.
• A simple improvement uses O(m + n) space, but still not the best solution.
• Could you devise a constant space solution?

Solution

# @param {Integer[][]} matrix
# @return {Void} Do not return anything, modify matrix in-place instead.
def set_zeroes(matrix)
  result = []
  m = matrix.length
  n = matrix[0].length

  (0...m).each do |i|
    (0...n).each do |j|
      result << [i, j] if matrix[i][j] == 0
    end
  end

  result.each do |r, c|
    (0...n).each do |i|
      matrix[r][i] = 0
    end
    (0...m).each do |j|
      matrix[j][c] = 0
    end
  end
  matrix
end

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